Tactile sense - Biology-Online Dictionary Definition noun The sense of touch where contact , pressure or traction exerted on the skin as well as in some internal organs are recognized. Supplement The tactile sense is one of the five traditional senses of the body . It is recognized by the organs of touch which are found mainly in the skin . The sensitivity varies from one part of the skin to another, e.g. the highly sensitive areas are the tactile sense on the forehead , temples , and the back of the forearm (H. N. Martin). Tactile sense is focused mainly on sense of pressure , traction and touch , excluding temperature and pain . Word origin: tactile : Latin tāctilis, from tāctus, ( touch ) + sense Synonym(s): Tactile - definition of tactile by The Free Dictionary Tactile - definition of tactile by The Free Dictionary 1. Relating to, involving, or perceptible to the sense of touch: tactile sensations; tactile sensitivity. 2. Characterized by or conveying an illusion of tangibility: tactile language. [From Latin tāctilis, from tāctus, past participle of tangere, to touch; see tact.] tac′tile·ly adv.

tac·til′i·ty (-tĭl′ĭ-tē) n. tactile (ˈtæktaɪl) adj 1. (Biology) of, relating to, affecting, or having a sense of touch: a tactile organ; tactile stimuli. 2. rare capable of being touched; tangible [C17: from Latin tactilis, from tangere to touch] tactility n 1. pertaining to or affecting the sense of touch. 2. perceptible to the touch; tangible. [1605–15; < Latin tāctilis tangible =ta(n)g(ere) to touch + -tilis -tile ] tac•til′i•ty (-ˈtɪl ɪ ti) n. tac·tile Used for or sensitive to touch: tactile organs. ThesaurusAntonymsRelated WordsSynonymsLegend: Adj. 1.

tactile - of or relating to or proceeding from the sense of touch; "haptic data"; "a tactile reflex" tangible , touchable - perceptible by the senses especially the sense of touch; "skin with a tangible roughness" tactile [ˈtæktaɪl] adj [experience, sensation] → tactile tactile adj → Tast- , taktil (spec); (= tangible) → greifbar , fühlbar ; (form: = gained by touching) stimulation, experience → durch Berührung erfolgend ; tactile sense → Tastsinn m; tactile organ → Tastorgan nt; she is a very tactile person → sie ist ein Mensch , der gern Körperkontakt hat; a more tactile society → eine Gesellschaft , in der Körperkontakte eine größere Rolle spielen (= interesting to touch) a tactile fabric → angenehm anzufühlende Stoffe tactile a. táctil, palpable; rel. al sentido del tacto; ___ discrimination → discriminación ___; tactile adj táctil Want to thank TFD for its existence? Tell a friend about us , add a link to this page, or visit the webmaster's page for free fun content .

Link to this page: esthesiometer References in classic literature ? The hands were always malformed; and though some surprised me by their unexpected human appearance, almost all were deficient in the number of the digits, clumsy about the finger-nails, and lacking any tactile sensibility. View in context Over such trivialities as these many a valuable hour may slip away, and the traveller who has gone to Italy to study the tactile values of Giotto, or the corruption of the Papacy, may return remembering nothing but the blue sky and the men and women who live under it. Of course, it contained frescoes by Giotto, in the presence of whose tactile values she was capable of feeling what was proper. It is so wonderful what they say about his tactile values. Tactile | Definition of Tactile by Merriam-Webster See tactile defined for kids Examples of tactile in a sentence He not only had visual difficulties but tactile ones, too—witness his grasping his wife's head and mistaking it for a hat … —Oliver Sacks, New Yorker, 7 Oct.

2002 There is a tactile and therefore somatic dimension to stroking the chalk that keeps the artist in constant, responsible and responsive touch with his emerging creation. —Jed Perl, New Republic, 17 June 2002 The keyboard has good tactile feedback, and the touch pad is responsive without being too twitchy. —Bruce Brown, PC Magazine, 20 Feb. 2001 … nothing prepared me for the tactile reality of the original volumes, leaf after carefully written leaf over which his hand had travelled … —Edmund Morris, New Yorker, 16 Jan. 1995 Near midday the heat of the sun bounced up from the bare patches of soil to hit with an almost tactile force. —Edward O. Wilson, Smithsonian, October 1984 The thick brushstrokes give the painting a tactile quality. Did You Know? Tangible is related to tactile, and so are intact , tact , contingent , tangent , and even entire .

There's also the uncommon noun taction , meaning "the act of touching." Like tactile, all of these words can be traced back to the Latin verb tangere, meaning "to touch." Tactile was adopted by English speakers in the early 17th century (possibly by way of the French tactile) from the Latin adjective tactilis ("tangible"). Tactilis comes from tactus, a past participle of tangere. Origin and Etymology of tactile French or Latin; French, from Latin tactilis, from tangere to touch — more at tangent First Known Use: 1615 Tactile | Define Tactile at Dictionary.com tactile [tak-til, -tahyl] /ˈtæk tɪl, -taɪl/ Spell of, pertaining to, endowed with, or affecting the sense of touch. 2. perceptible to the touch; tangible.

Origin of tactile 1605-15; < Latin tāctilis tangible, equivalent to tāct(us) (past participle of tangere to touch) + -ilis -ile Related forms [tak-til-i-tee] /tækˈtɪl ɪ ti/ (Show IPA), noun nontactile, adjective Examples from the Web for tactile Expand Zodiac Beast: May 1-7 Starsky + Cox April 29, 2011 These tactile projects make them “feel they can start and finish something,” she said. The Planet Strappers Raymond Zinke Gallun tactile: used for touching; an organ that has the sense of touch. British Dictionary definitions for tactile Expand of, relating to, affecting, or having a sense of touch: a tactile organ, tactile stimuli 2. (rare) capable of being touched; tangible Derived Forms C17: from Latin tactilis, from tangere to touch Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd.

1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for tactile Expand adj. 1610s, "perceptible to touch," from French tactile, from Latin tactilis "tangible, that may be touched," from tactus, past participle of tangere "to touch" (see tangent ). Meaning "of or pertaining to touch" is attested from 1650s. Online Etymology Dictionary, © 2010 Douglas Harper Impact on the Senses - Tactile SPD Information Symptoms Impact on the Senses Impact on the Senses The Tactile (Touch) Sense Overview of the Tactile Sense Like any other sensory system, the tactile sense can become an issue for people suffering from Sensory Processing Disorder. The tactile sense is received through millions of nerve ending on the skin, detecting even the slightest touch sensations and reporting it to the brain.

In a well regulated tactile system, the vast majority of these sensations are gaited, creating the ability for the person to notice, but not respond to, very minute changes in wind speed, outside temperature, or very light touch. Once the brain receives this information, it responds accordingly, monitoring only those tactile sensations it perceives accurately to be dangerous or threatening. Therefore, this person will only be sent into fight or flight over aggressive attacks, like punching, kicking, or scratching. They usually won't be easily aggravated by most clothing tags, types of fabric, or waistbands; and being lightly touched will not be a problem. They won't be excessively ticklish, and won't withdraw or strike out when being unexpectedly touched. They will also have preferences in textures of clothing and food, but most likely won't excessively seek out certain types of clothing. Tactile Defensiveness If a person is an over-responder to tactile sensations, they are referred to as tactile defensive, and their brain will not accurately perceive touch sensations. Their brains may not gait touch sensations, so they may be sent into fight or flight over very small, everyday touch sensations.

Being bumped, nudged, or poked unexpectedly, especially if the person or object that is touching them cannot be seen or otherwise anticipated, can send them into an uncontrollable and inappropriate fight or flight response. Without expecting the touch, their brain may interpret it incorrectly as a threat, which can cause them to startle easily, jump away, or even lash out at someone for touching them. Getting splashed by water or having an unexpected or unwanted change in temperature can also lead to a fight or flight response. Small changes in outside temperature and wind speed are often noticeable and can have a large effect. Their eyes might also be very sensitive and they will often need to blink at the slightest amount of cold wind. Their brain will also have a hard time habituating certain touch sensations. A clothing tag can lead to constant agitation, and is often said to 'feel like an irremovable spider'. Stitching in seems may feel like thousands of needles poking into the skin, as every stitch can be felt as irritating, creating a burning sensation. People with tactile defensiveness have a hard time finding socks, underwear, and shirts as the seams are actually perceived as painful.

Most clothes will feel too tight, and cause a sensation of being overheated, which becomes almost impossible not to focus on. They will often fidget with and adjust their clothing. While alone, they may prefer nudity, although even a slight breeze can also be perceived as agitating against the skin. Deep pressure against the skin can be helpful, but light touch is always perceived as burning, tickling, or scratching. This may cause a withdrawal from intimacy, or may lead to them only wanting it on their terms. Tactile defensives will often avoid gritty sensations, such as sand and dirt. It may also take a very long time to get used to water temperature when they go swimming and their face may feel as though it is burning when it is underwater. Poor hygiene, caused by aggravation during skin washing, bathing, hair washing, hair cutting and brushing, nail clipping, deodorant, and shaving, frequently occur. Tactile Under-Responsiveness People who are hyposensitive to tactile input often can't feel large changes in temperature or wind on their body. The brain may inappropriately gait even dangerous feelings, such as heavy impacts and being cut.

The sufferer may not even feel or respond to having been hit, or having cut themselves, which can be dangerous to their health, and may not allow them to respond appropriately to being physically assaulted. They may also sit on objects frequently without even noticing them. Tactile Seeking Tactile sensory seekers often seek out tactile sensations, like playing with sand and muck. They may lather certain things on their body to achieve the stimulation they are craving on their skin. They may run their hands or fingers across walls, railings, or other objects in their environment. It is also common for them to constantly touch other people. Tactile seekers may have a hard time refraining from grabbing and handling everything, which is often viewed as bad behavior or a character flaw. Tactile Discrimination Disorder Tactile discrimination allows an individual to know where they are being touched, how firmly they are being touched, and what they are touching if they are the one touching. Tactile Discrimination Disorder directly impacts a person's ability to do this. People with tactile discrimination disorder will have a hard time knowing where they are being touched, especially when they can not see what is touching them. They will have difficulty pinpointing where they are being touched, as well.

Difficulty with tactile discrimination will also impair a person's ability to know what they are touching without looking. They will need to use their eyes when searching through their pockets, purse, or bags because they cannot tell what they are handling unless they look. Aging changes in the senses: MedlinePlus Medical Encyclopedia Watch this video about: Hearing and the cochlea Balance (equilibrium) is controlled in the inner ear. Fluid and small hairs in the inner ear stimulate the auditory nerve. This helps the brain maintain balance. As you age, structures inside the ear start to change and their functions decline. Your ability to pick up sounds decreases. You may also have problems maintaining your balance as you sit, stand, and walk. Age-related hearing loss is called presbycusis . It affects both ears. Hearing, especially of high-frequency sounds, may decline. You may also have trouble telling the difference between certain sounds. Or, you may have problems hearing a conversation when there is background noise. If you are having trouble hearing, discuss your symptoms with your health care provider. One way to manage hearing loss is by getting fitted with hearing aids. Persistent, abnormal ear noise ( tinnitus ) is another common problem in older adults.

Causes of tinnitus may include wax buildup or medicines that damage structures inside the ear. If you have tinnitus, ask your health care provider how to manage the condition. Impacted ear wax can also cause trouble hearing and is common with age. Your health care provider can remove impacted ear wax. VISION Vision occurs when light is processed by your eye and interpreted by your brain. Light passes through the transparent eye surface (cornea). It continues through the pupil, the opening to the inside of the eye. The pupil becomes larger or smaller to control the amount of light that enters the eye. The colored part of the eye is called the iris . It is a muscle that controls pupil size. After light passes through your pupil, it reaches the lens. The lens focuses light on your retina (the back of the eye). The retina converts light energy into a nerve signal that the optic nerve carries to the brain, where it is interpreted. Watch this video about: Seeing All of the eye structures change with aging. The cornea becomes less sensitive, so you might not notice eye injuries. By the time you turn 60, your pupils may decrease to about one third of the size they were when you were 20.

The pupils may react more slowly in response to darkness or bright light. The lens becomes yellowed, less flexible, and slightly cloudy. The fat pads supporting the eyes decrease and the eyes sink into their sockets. The eye muscles become less able to fully rotate the eye. As you age, the sharpness of your vision ( visual acuity ) gradually declines. The most common problem is difficulty focusing the eyes on close-up objects. This condition is called called presbyopia . Reading glasses, bifocal glasses, or contact lenses can help correct presbyopia. You may be less able to tolerate glare. For example, glare from a shiny floor in a sunlit room can make it difficult to get around indoors. You may have trouble adapting to darkness or bright light. Problems with glare, brightness, and darkness may make you give up driving at night. As you age, it gets harder to tell blues from greens than it is to tell reds from yellows. Using warm contrasting colors (yellow, orange, and red) in your home can improve your ability to see. Keeping a red light on in darkened rooms, such as the hallway or bathroom, makes it easier to see than using a regular night light.

With aging, the gel-like substance (vitreous) inside your eye starts to shrink. This can create small particles called floaters in your field of vision. In most cases, floaters do not reduce your vision. But if you develop floaters suddenly or have a rapid increase in the number of floaters, you should have your eyes checked by a professional. Reduced peripheral vision (side vision) is common in older people. This can limit your activity and ability to interact with others. It may be hard to communicate with people sitting next to you because you cannot see them well. Driving can become dangerous. Weakened eye muscles may prevent you from moving your eyes in all directions. It may be hard to look upward. The area in which objects can be seen ( visual field ) gets smaller. Aging eyes also may not produce enough tears. This leads to dry eyes. When dry eyes are not treated, infection, inflammation, and scarring of the cornea can occur. You can relieve dry eyes by using eye drops or artificial tears.

Common eye disorders that cause vision changes that are NOT normal include: Cataracts -- clouding of the lens of the eye Glaucoma -- rise in fluid pressure in the eye Macular degeneration -- disease in the macula (responsible for central vision) that causes vision loss Retinopathy -- disease in the retina caused by diabetes or high blood pressure If you are having vision problems, discuss your symptoms with your health care provider. TASTE AND SMELL The senses of taste and smell work together. Most tastes are linked with odors. The sense of smell begins at the nerve endings high in the lining of the nose. Watch this video about: Smelling You have about 9,000 taste buds. Your taste buds sense sweet, salty, sour, bitter, and umami flavors. Umami is a taste linked with foods that contain glutamate, such as the seasoning monosodium glutamate (MSG). Watch this video about: Tasting Smell and taste play a role in food enjoyment and safety. A delicious meal or pleasant aroma can improve social interaction and enjoyment of life. Smell and taste also allow you to detect danger, such as spoiled food, gases, and smoke. The number of taste buds decreases as you age.

Each remaining taste bud also begins to shrink. Sensitivity to the 5 tastes often declines after age 60. In addition, your mouth produces less saliva as you age. This can cause dry mouth, which can affect your sense of taste. Your sense of smell can also diminish, especially after age 70. This may be related to a loss of nerve endings and less mucus production in the nose. Mucus helps odors stay in the nose long enough to be detected by the nerve endings. It also helps clear odors from the nerve endings. Certain things can speed up the loss of taste and smell. These include diseases, smoking, and exposure to harmful particles in the air. Decreased taste and smell can lessen your interest and enjoyment in eating. You may not be able to sense certain dangers if you cannot smell odors such as natural gas or smoke from a fire. If your senses of taste and smell have diminished, talk to your health care provider. The following may help: Switch to a different medicine, if the medicine you take is affecting your ability to smell and taste. Use different spices or change the way you prepare food. Buy safety products, such as a gas detector that sounds an alarm you can hear.

TOUCH, VIBRATION, AND PAIN The sense of touch makes you aware of pain, temperature, pressure, vibration, and body position. Skin, muscles, tendons, joints, and internal organs have nerve endings (receptors) that detect these sensations. Some receptors give the brain information about the position and condition of internal organs. Though you may not be aware of this information, it helps to identify changes (for example, the pain of appendicitis ). Your brain interprets the type and amount of touch sensation. It also interprets the sensation as pleasant (such as being comfortably warm), unpleasant (such as being very hot), or neutral (such as being aware that you are touching something). Watch this video about: Feeling pain With aging, sensations may be reduced or changed. These changes can occur because of decreased blood flow to the nerve endings or to the spinal cord or brain. The spinal cord transmits nerve signals and the brain interprets these signals. Health problems, such as a lack of certain nutrients, can also cause sensation changes. Brain surgery, problems in the brain, confusion, and nerve damage from injury or chronic diseases such as diabetes can also result in sensation changes. Symptoms of changed sensation vary based on the cause.

With decreased temperature sensitivity, it can be hard to tell the difference between cool and cold and hot and warm. This can increase the risk of injury from frostbite , hypothermia (dangerously low body temperature), and burns . Reduced ability to detect vibration, touch, and pressure increases the risk of injuries, including pressure ulcers (skin sores that develop when pressure cuts off blood supply to the area). After age 50, many people have reduced sensitivity to pain. Or you may feel and recognize pain, but it does not bother you. For example, when you are injured, you may not know how severe the injury is because the pain does not trouble you. You may develop problems walking because of reduced ability to perceive where your body is in relation to the floor. This increases your risk of falling, a common problem for older people. Older people can become more sensitive to light touches because their skin is thinner. If you have noticed changes in touch, pain, or problems standing or walking, talk with your health care provider. There may be ways to manage the symptoms. The following measures can help you stay safe: Lower the water heater temperature to no higher than 125°F (51°C) to avoid burns.

Check the thermometer to decide how to dress, rather than waiting until you feel overheated or chilled. Inspect your skin, especially your feet, for injuries. If you find an injury, treat it. Do not assume the injury is not serious because the area is not painful. OTHER CHANGES Skin & Sense of Touch | Science Newsletter Sign Up for Our Newsletter: Submit Our skin acts as the protective barrier between our internal body systems and the outside world. Its ability to perceive touch sensations gives our brains a wealth of information about the environment around us, such as temperature, pain, and pressure. Without our sense of touch, it would be very hard to get around in this world! We wouldn't feel our feet hitting the floor when we walked, we wouldn't sense when something sharp cut us, and we wouldn't feel the warm sun on our skin. It is truly amazing how much information we receive about the world through our sense of touch, and although we still don't know all the ins and outs of how the skin perceives touch, what we do know is interesting. Skin Anatomy The skin is composed of several layers. The very top layer is the epidermis and is the layer of skin you can see.

In Latin, the prefix "epi-" means "upon" or "over." So the epidermis is the layer upon the dermis (the dermis is the second layer of skin). Made of dead skin cells, the epidermis is waterproof and serves as a protective wrap for the underlying skin layers and the rest of the body. It contains melanin, which protects against the sun's harmful rays and also gives skin its color. When you are in the sun, the melanin builds up to increase its protective properties, which also causes the skin to darken. The epidermis also contains very sensitive cells called touch receptors that give the brain a variety of information about the environment the body is in. The second layer of skin is the dermis. The dermis contains hair follicles, sweat glands, sebaceous (oil) glands, blood vessels, nerve endings, and a variety of touch receptors. Its primary function is to sustain and support the epidermis by diffusing nutrients to it and replacing the skin cells that are shed off the upper layer of the epidermis.

New cells are formed at the junction between the dermis and epidermis, and they slowly push their way towards the surface of the skin so that they can replace the dead skin cells that are shed. Oil and sweat glands eliminate waste produced at the dermis level of the skin by opening their pores at the surface of the epidermis and releasing the waste. The bottom layer is the subcutaneous tissue which is composed of fat and connective tissue. The layer of fat acts as an insulator and helps regulate body temperature. It also acts as a cushion to protect underlying tissue from damage when you bump into things. The connective tissue keeps the skin attached to the muscles and tendons underneath. Somatosensory System: The Ability To Sense Touch Our sense of touch is controlled by a huge network of nerve endings and touch receptors in the skin known as the somatosensory system. This system is responsible for all the sensations we feel - cold, hot, smooth, rough, pressure, tickle, itch, pain, vibrations, and more. Within the somatosensory system, there are four main types of receptors: mechanoreceptors, thermoreceptors, pain receptors, and proprioceptors.

Before we dig further into these specialized receptors, it is important to understand how they adapt to a change in stimulus (anything that touches the skin and causes sensations such as hot, cold, pressure, tickle, etc). A touch receptor is considered rapidly adapting if it responds to a change in stimulus very quickly. Basically this means that it can sense right away when the skin is touching an object and when it stops touching that object. However, rapidly adapting receptors can't sense the continuation and duration of a stimulus touching the skin (how long the skin is touching an object). These receptors best sense vibrations occurring on or within the skin. A touch receptor is considered slowly adapting if it does not respond to a change in stimulus very quickly. These receptors are very good at sensing the continuous pressure of an object touching or indenting the skin but are not very good at sensing when the stimulus started or ended. Mechanoreceptors: These receptors perceive sensations such as pressure, vibrations, and texture. There are four known types of mechanoreceptors whose only function is to perceive indentions and vibrations of the skin: Merkel's disks, Meissner's corpuscles, Ruffini's corpuscles, and Pacinian corpuscles.

The most sensitive mechanoreceptors, Merkel's disks and Meissner's corpuscles, are found in the very top layers of the dermis and epidermis and are generally found in non-hairy skin such as the palms, lips, tongue, soles of feet, fingertips, eyelids, and the face. Merkel's disks are slowly adapting receptors and Meissner's corpuscles are rapidly adapting receptors so your skin can perceive both when you are touching something and how long the object is touching the skin. Your brain gets an enormous amount of information about the texture of objects through your fingertips because the ridges that make up your fingerprints are full of these sensitive mechanoreceptors. Located deeper in the dermis and along joints, tendons, and muscles are Ruffini's corpuscles and Pacinian corpuscles. These mechanoreceptors can feel sensations such as vibrations traveling down bones and tendons, rotational movement of limbs, and the stretching of skin. This greatly aids your ability to do physical activities such as walking and playing ball. Thermoreceptors: As their name suggests, these receptors perceive sensations related to the temperature of objects the skin feels. They are found in the dermis layer of the skin.

There are two basic categories of thermoreceptors: hot and cold receptors. Cold receptors start to perceive cold sensations when the surface of the skin drops below 95 ° F. They are most stimulated when the surface of the skin is at 77 ° F and are no longer stimulated when the surface of the skin drops below 41 ° F. This is why your feet or hands start to go numb when they are submerged in icy water for a long period of time. Hot receptors start to perceive hot sensations when the surface of the skin rises above 86 ° F and are most stimulated at 113 ° F. But beyond 113 ° F, pain receptors take over to avoid damage being done to the skin and underlying tissues. Thermoreceptors are found all over the body, but cold receptors are found in greater density than heat receptors. The highest concentration of thermoreceptors can be found in the face and ears (hence why your nose and ears always get colder faster than the rest of your body on a chilly winter day). Pain receptors: The scientific term is nocireceptor.

"Noci-" in Latin means "injurious" or "hurt" which is a good clue that these receptors detect pain or stimuli that can or does cause damage to the skin and other tissues of the body. There are over three million pain receptors throughout the body, found in skin, muscles, bones, blood vessels, and some organs. They can detect pain that is caused by mechanical stimuli (cut or scrape), thermal stimuli (burn), or chemical stimuli (poison from an insect sting). These receptors cause a feeling of sharp pain to encourage you to quickly move away from a harmful stimulus such as a broken piece of glass or a hot stove stop. They also have receptors that cause a dull pain in an area that has been injured to encourage you not to use or touch that limb or body part until the damaged area has healed. While it is never fun to activate these receptors that cause pain, they play an important part in keeping the body safe from serious injury or damage by sending these early warning signals to the brain.

Proprioceptors: In Latin, the word "proprius" means "one's own" and is used in the name of these receptors because they sense the position of the different parts of the body in relation to each other and the surrounding environment. Proprioceptors are found in tendons, muscles, and joint capsules. This location in the body allows these special cells to detect changes in muscle length and muscle tension. Without proprioceptors, we would not be able to do fundamental things such as feeding or clothing ourselves. While many receptors have specific functions to help us perceive different touch sensations, almost never are just one type active at any one time. When drinking from a freshly opened can of soda, your hand can perceive many different sensations just by holding it. Thermoreceptors are sensing that the can is much colder than the surrounding air, while the mechanoreceptors in your fingers are feeling the smoothness of the can and the small fluttering sensations inside the can caused by the carbon dioxide bubbles rising to the surface of the soda. Mechanoreceptors located deeper in your hand can sense that your hand is stretching around the can, that pressure is being exerted to hold the can, and that your hand is grasping the can.

Proprioceptors are also sensing the hand stretching as well as how the hand and fingers are holding the can in relation to each other and the rest of the body. Even with all this going on, your somatosensory system is probably sending even more information to the brain than what was just described. Nerve Signals: Making Sense of It All Of course, none of the sensations felt by the somatosensory system would make any difference if these sensations could not reach the brain. The nervous system of the body takes up this important task. Neurons (which are specialized nerve cells that are the smallest unit of the nervous system) receive and transmit messages with other neurons so that messages can be sent to and from the brain. This allows the brain to communicate with the body. When your hand touches an object, the mechanoreceptors in the skin are activated, and they start a chain of events by signaling to the nearest neuron that they touched something. This neuron then transmits this message to the next neuron which gets passed on to the next neuron and on it goes until the message is sent to the brain.

Now the brain can process what your hand touched and send messages back to your hand via this same pathway to let the hand know if the brain wants more information about the object it is touching or if the hand should stop touching it. Is the Glass of Water Hot or Cold? With this experiment, test your skin's ability to perceive whether an object is hot or cold. What You Need: Three tall glasses of water, one filled with very warm or hot water (not burning), one filled with room-temperature water, and one filled with ice water A clock to time yourself What You Do: Grab the glass of hot water with one hand, making sure that your palm is touching the glass. Grab the glass of ice water with your other hand, holding the glass in a similar fashion. Hold the glasses for at least 60 seconds. After holding the hot and cold glasses for 60 seconds, grab the room-temperature glass with both hands, palms touching the glass. Does the glass of room-temperature water feel hot or cold? What Happened: Your brain just received confusing messages from your hands about what the temperature of the third glass was.

The hand originally holding the hot glass told you the third glass was cold, whereas the hand originally holding the cold glass told you the third glass was hot. But they were both touching the same glass. How can this be? You received these confusing messages because our skin does not perceive the exact temperature of an object. Instead, your skin can sense the difference in temperature of a new object in comparison to the temperature of an object the skin was already used to ("relative temperature"). This is why entering a body of water, such as a pool or lake, seems really cold at first (your body was used to the warmer air) but then gradually "warms up" after being in the water for a while (your body adjusts to the temperature of the water). Two-Point Discrimination Is your skin equally sensitive all over your body? Try this experiment to find out more about how well your skin perceives touch. What You Need: Ruler that measures in millimeters Two toothpicks Prepare for this activity by setting up a chart like the one listed above. You may need to go beyond 10 mm in this activity, and you may want to test more areas of the body than what is listed.

Some suggestions are: back of finger, back of hand, wrist, neck, stomach, top of foot, sole of foot, calf, thigh, forehead, nose, lip, and ear. Explain to your partner that you are going to lightly poke her with either one or two toothpicks on various places on her skin. Her job is to tell you whether or not she feels one poke or two pokes. To make sure she is not cheating, she needs to either wear a blindfold or keep her eyes closed. Without telling your partner this, hold the two toothpicks so that the points measure 1 mm apart and lightly poke her on the palm of her hand. Ask her if she felt one or two points on her skin. If she says one point, separate the two points of the toothpicks so that they measure 2 mm apart and lightly poke her in the palm again. Keep pulling the points apart until she says that she feels two points. Record the measurement at which she felt points on the palm of her hand. Repeat step 3 with other parts of the body, such as the fingertips, the upper arm, the back, the stomach, the face, the legs, and feet.

Make sure to record the smallest distance at which each area of the body felt two distinct points when poked with the toothpicks. What Happened: The ability to distinguish between one point or two points of sensation depends on how dense mechanoreceptors are in the area of the skin being touched. You most likely found that certain areas of your body are much more sensitive to touch than other areas. Highly sensitive areas such as the fingertips and tongue can have as many as 100 pressure receptors in one cubic centimeter. Less sensitive areas, such as your back, can have as few as 10 pressure receptors in one cubic centimeter. Because of this, areas such as your back are much less responsive to touch and can gather less information about what is touching it than your fingertips can. Science in the News When a person loses an arm or a leg in an accident, they not only lose that limb, they also lose all the touch sensations that were received through that limb. Many amputees (people who have lost a limb) receive prosthetic (artificial) limbs to help regain some of the function and mobility they had before they lost the limb.

However, conventional prosthetic limbs couldn't let the person feel when he grabbed hold of an object or when her foot touched the ground, making it a struggle for most amputees to successfully use a prosthetic limb for everyday purposes. But scientists are making leaps and bounds in helping people regain mobility and sensation after losing a limb. The goal is to someday give amputees prosthetic limbs that will allow them to use only nerve signals from the brain to control the prosthetic limb, and have the limb send touch information back to the brain to make control over the limb a little easier. That someday is getting closer. Claudia Mitchell, a former US marine who lost her arm in a motorcycle accident, is one of the most recent people to receive such an advanced prosthetic limb. Her new limb has been connected to the motor and sensory nerves in her chest that once controlled her real limb and now control her new arm. While it is still limited in what it can feel and do, this new limb allows Claudia to feel touch and heat, and she can perform conventional tasks (such as folding laundry and cutting up vegetables) four times faster than she could with a regular prosthetic limb. To read more about Claudia and her bionic arm, click here .

Fabulous Facts What's the largest organ of your body? You may be surprised to find out it is your skin. The skin makes up about 15% of your body weight - if you weigh 100 pounds, 15 of those pounds come from your skin. Measured in surface area, the skin averages 20 square feet in adults. Skin is constantly renewing itself, which is a good thing since you shed 50 million skin cells every day - that's about 30,000 to 40,000 skin cells every minute. Science Links Learn more about the skin's structure and function . Be sure to check out the "Structure of the skin" and "What does the skin do?" links to see animated clips on how the skin renews itself and senses temperature changes. For more information on how well different areas of your body perceive touch sensations, take a look at this animated version of a homunculus , which is a map of the body drawn in proportion to how much information the brain receives about touch from the different parts of the body. Human Sense Organs - The Five Senses and some amazing optical illusions. Hearing. The ear is the organ of hearing.

The outer ear protrudes away from the head and is shaped like a cup to direct sounds toward the tympanic membrane, which transmits vibrations to the inner ear through a series of small bones in the middle ear called the malleus, incus and stapes. The inner ear, or cochlea, is a spiral-shaped chamber covered internally by nerve fibers that react to the vibrations and transmit impulses to the brain via the auditory nerve. The brain combines the input of our two ears to determine the direction and distance of sounds. The inner ear has a vestibular system formed by three semicircular canals that are approximately at right angles to each other and which are responsible for the sense of balance and spatial orientation. The inner ear has chambers filled with a viscous fluid and small particles (otoliths) containing calcium carbonate. The movement of these particles over small hair cells in the inner ear sends signals to the brain that are interpreted as motion and acceleration. The human ear can perceive frequencies from 16 cycles per second, which is a very deep bass, to 28,000 cycles per second, which is a very high pitch. Bats and dolphins can detect frequencies higher than 100,000 cycles per second.

The human ear can detect pitch changes as small as 3 hundredths of one percent of the original frequency in some frequency ranges. Some people have "perfect pitch", which is the ability to map a tone precisely on the musical scale without reference to an external standard. It is estimated that less than one in ten thousand people have perfect pitch, but speakers of tonal languages like Vietnamese and Mandarin show remarkably precise absolute pitch in reading out lists of words because pitch is an essential feature in conveying the meaning of words in tone languages. The Eguchi Method teaches perfect pitch to children starting before they are 4 years old. After age 7, the ability to recognize notes does not improve much. Taste. The receptors for taste, called taste buds, are situated chiefly in the tongue, but they are also located in the roof of the mouth and near the pharynx. They are able to detect four basic tastes: salty, sweet, bitter, and sour. The tongue also can detect a sensation called "umami" from taste receptors sensitive to amino acids. Generally, the taste buds close to the tip of the tongue are sensitive to sweet tastes, whereas those in the back of the tongue are sensitive to bitter tastes.

The taste buds on top and on the side of the tongue are sensitive to salty and sour tastes. At the base of each taste bud there is a nerve that sends the sensations to the brain. The sense of taste functions in coordination with the sense of smell. The number of taste buds varies substantially from individual to individual, but greater numbers increase sensitivity. Women, in general, have a greater number of taste buds than men. As in the case of color blindness, some people are insensitive to some tastes. Smell. The nose is the organ responsible for the sense of smell. The cavity of the nose is lined with mucous membranes that have smell receptors connected to the olfactory nerve. The smells themselves consist of vapors of various substances. The smell receptors interact with the molecules of these vapors and transmit the sensations to the brain. The nose also has a structure called the vomeronasal organ whose function has not been determined, but which is suspected of being sensitive to pheromones that influence the reproductive cycle. The smell receptors are sensitive to seven types of sensations that can be characterized as camphor, musk, flower, mint, ether, acrid, or putrid. The sense of smell is sometimes temporarily lost when a person has a cold.

Dogs have a sense of smell that is many times more sensitive than man's. Touch. The sense of touch is distributed throughout the body. Nerve endings in the skin and other parts of the body transmit sensations to the brain. Some parts of the body have a larger number of nerve endings and, therefore, are more sensitive. Four kinds of touch sensations can be identified: cold, heat, contact, and pain. Hairs on the skin magnify the sensitivity and act as an early warning system for the body. The fingertips and the sexual organs have the greatest concentration of nerve endings. The sexual organs have "erogenous zones" that when stimulated start a series of endocrine reactions and motor responses resulting in orgasm. Beyond the five sense organs. In addition to sight, smell, taste, touch, and hearing, humans also have awareness of balance (equilibrioception), pressure, temperature (thermoception), pain (nociception), and motion all of which may involve the coordinated use of multiple sensory organs. The sense of balance is maintained by a complex interaction of visual inputs, the proprioceptive sensors (which are affected by gravity and stretch sensors found in muscles, skin, and joints), the inner ear vestibular system, and the central nervous system.

Disturbances occurring in any part of the balance system, or even within the brain's integration of inputs, can cause the feeling of dizziness or unsteadiness. Kinesthesia is the precise awareness of muscle and joint movement that allows us to coordinate our muscles when we walk, talk, and use our hands. It is the sense of kinesthesia that enables us to touch the tip of our nose with our eyes closed or to know which part of the body we should scratch when we itch. Synesthesia. Some people experience a phenomenon called synesthesia in which one type of stimulation evokes the sensation of another. For example, the hearing of a sound may result in the sensation of the visualization of a color, or a shape may be sensed as a smell. Synesthesia is hereditary and it is estimated that it occurs in 1 out of 1000 individuals with variations of type and intensity. The most common forms of synesthesia link numbers or letters with colors. Next

Question: Tactile relates to which of the senses?
Answer: Touch